Keywords: historical masonry tower, masonry structure, modal properties, dynamic response..

The fundamental period of vibration plays a primary role in the assessment of the seismic demand on structures. A reliable evaluation of dynamic and seismic response of structures requires an accurate estimation of their modal properties. This is a relevant aspect for both the design of new structures and the assessment and strengthening of existing ones. In the case of historical structures the accuracy of numerical analysis is critical because interventions have to be carefully calibrated in order to limit their invasiveness.

Structural modal properties can be obtained from an eigenvalue analysis of its mechanical model, or either from empirical correlations as a function of geometric parameters (usually the height), whenever prescribed regularity conditions are fulfilled.

In this paper, starting from available experimental results from output-only modal identification tests on ancient masonry towers in the Molise region, of Southern Italy, numerical analyses were performed with the aim of investigating the relevant factors influencing the structural dynamic response of the towers described in this paper. A numerical procedure able to solve an eigenvalue problem for a Timoshenko beam has been developed and used to carry out extensive sensitivity analyses.

The final objective of the analyses described in this paper, was the quantitative assessment of the influence of the relevant geometric and mechanical parameters on the dynamic response of historical masonry towers. The aim was the development of a formulation for the prediction of the fundamental period as a function of the height, based on the analogy with similar correlations reported in the literature and in design codes for selected structural typologies.

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